package cn.njxzc.examples;

class Aa {
	String a = "class A";
}

class Bb extends Aa {
	String b = "class B";
}

class Exam3_17 {
	public static void main(String[] args) {
		Aa a1, a2 = new Aa();
		Bb b1, b2 = new Bb();
		a1 = b2;
		b1 = (Bb) a1;
		System.out.println(a1.a);
		System.out.println(b1.b);
	}

}